STEREO-B Status Update

Communications with Solar Terrestrial Relations Observatory-B (STEREO-B) were lost on Oct. 1, 2014, due to multiple hardware anomalies affecting control of the spacecraft orientation. Communications with STEREO-B were re-established on Aug. 21, 2016, during a monthly attempt to reach the spacecraft using NASA's Deep Space Network. During the next weeks, the NASA and the Johns Hopkins APL STEREO teams worked tirelessly to discover the spacecraft's current conditions and to recover the spacecraft fully. The attempt to recover the spacecraft was not successful. STEREO-B has now been out of contact since Sept. 23, 2016. Four years after the initial loss of communications anomaly with the Behind observatory, NASA directed that periodic recovery operations cease with the last support on October 17, 2018.

• LOSS HISTORY: Communications with STEREO-B were lost on Oct. 1, 2014, during a test of the spacecraft's command loss timer, a hard reset that is triggered after the spacecraft goes without communications from Earth for 72 hours. This test was in preparation for STEREO to be out of contact with Earth as it passed behind the sun. This event is known as solar conjunction and disrupts the DSN's ability to communicate with the spacecraft; as conjunction occurred beyond STEREO's two-year design mission lifetime, STEREO had no design requirements anticipating periods of weeks without communications. During this two to three week period, STEREO's command loss timer would have expired multiple times.

• RECOVERY ATTEMPTS: After a persistent search and utilizing a special command sequence designed to interrupt a cycle of collapsing battery voltage, communications with STEREO-B were re-established on Aug. 21, 2016. During the next weeks, the STEREO team worked to learn more about the state of the spacecraft and to recover it. However, data was very limited; the large distance to the spacecraft (~2 AU) and the uncontrolled orientation meant that while the DSN could detect that STEREO-B was transmitting, very few packets of telemetry -- containing the on-board measurements of temperatures, voltages, etc. - were, in fact, received.
  
  With the limited data available, the team formulated a plan to attempt a recovery and stabilize the spacecraft pointing. The attempt was not successful. The limited data available during the recovery attempt revealed that STEREO-B came close to achieving a stable orientation, but one set of thrusters on-board may have performed abnormally, possibly due to frozen propellant and ultimately spun the spacecraft back up into an uncontrolled state. STEREO-B has now been out of contact since September 23. An attempt was made to optically search for the spacecraft as it presumably passed by Earth in the summer 2023, but this was unsuccessful, ending any chance of recovering STEREO-B.

• INFORMATION LEARNED: The 2016 contact with STEREO-B revealed new information about the spacecraft's rate of spin and precise location in space - which is particularly important since, when contact was lost, it wasn't clear if STEREO-B had fired its thrusters in such a way as to affect its expected orbit. Data from STEREO-B also shows that the spacecraft battery is operating with very low charge, a challenge made more difficult to overcome by the fact that STEREO-B's solar panels are no longer pointed directly at the sun, meaning that the battery charges only a fraction of the time. Mission operators also have new information about how STEREO-B responds to extreme conditions including both very high and low temperatures.

• STEREO BACKGROUND:
  • The Solar Terrestrial Relations Observatory is part of the Heliophysics Systems Observatory, a collection of missions that observes the sun and our space environment, providing research that contributes to the safety of spacecraft both in near-Earth space and as they travel further from home.
  • STEREO consists of two nearly identical spacecraft put into slightly different orbits around the sun - one moving faster than Earth, one moving more slowly - so they each have a different vantage point of the star.
  • Launched in October 2006, the STEREO mission design lifetime was two years. Having delivered far beyond expectations, the mission is now poised to enter its second decade of operations.
  • The STEREO mission was designed to provide the first-ever stereoscopic measurements of the sun, providing 3-dimensional views of the structure and evolution of eruptions on the sun - eruptions such as coronal mass ejections that can disrupt the space environment near Earth and interfere with radio communications and satellite electronics.
  • STEREO-A continues to operate normally. STEREO's current mission extension was based on using just one spacecraft, so, regardless of what happens with STEREO-B, the STEREO mission will provide robust solar research in the coming years.
    • Planned research is to characterize space weather throughout the inner heliosphere, support 360 degree coverage of the sun (along with SDO and SOHO) and improve our understanding of phenomena from the sun's atmosphere, all the way to the edges of the heliosphere.
  • STEREO is the third mission in NASA's Solar Terrestrial Probes program, which is managed by NASA Goddard for NASA's Heliophysics Division of the Science Mission Directorate, in Washington. The Johns Hopkins University Applied Physics Laboratory, in Laurel, Maryland, designed, built and operates the twin observatories.

Detailed updates about the recovery operations between August 21 and October 9, 2016, can be found on our What's New page.

The original message about the loss of contact with STEREO Behind can be found here.